JPS6141639B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention speeds up the growth of nitrifying microorganisms on the surface of the medium when nitrifying microorganisms convert ammonia nitrogen in raw water into nitrite nitrogen and nitrate nitrogen under aerobic conditions. This invention relates to a method for nitrification of wastewater that shortens the breeding period. The oxidation reaction of ammonia and nitrite by nitrifying microorganisms is as shown in the following equations (1) and (2). These reactions provide energy for nitrifying microbial growth. Empirical formula for microbial cells
If C ₅ H ₇ NO ₂ is assumed, the growth equation of nitrifying microorganisms is shown by the following equations (3) and (4). As shown in equations (3) and (4) above, nitrifying microorganisms, which are autotrophic bacteria, use ammonia nitrogen and inorganic carbon such as bicarbonate and carbonate for cell synthesis during growth, as well as other metals and phosphorus. , trace amounts of inorganic salts, etc. are required, but no organic substances are required. Therefore, even if raw water does not contain any BOD components, as long as it contains ammonia nitrogen and inorganic carbon necessary for cell synthesis, nitrification treatment can be performed under aerobic conditions. be. However, perhaps because nitrifying microorganisms secrete less viscous substances than BOD-degrading microorganisms, the viscosity of biological flocs and slime is low and their adhesion to the medium is poor. Conventionally, most nitrification treatments have been based on biological suspension methods such as the activated sludge method. With this biological suspension method, the adhesion of microorganisms to the medium is not a problem, so BOD in the raw water is
There was no effect on the population of nitrifying microorganisms even if the amount was less than 5mg/. However, the biological fixed bed method that has recently become popular, that is, biological treatment in which nitrifying microorganisms are grown on the surface of media such as sprinkled beds, immersed beds, and fluidized beds,
The targets of nitrification treatment are mostly treated sewage water, treated human waste water, etc., which contain more than 5 mg of BOD.
Moreover, since there were many BOD-degrading microorganisms present, the agglomeration of nitrifying microorganisms on the media surface was not a problem. However, in the nitrification treatment of industrial wastewater containing ammonia nitrogen with a BOD of 5mg/or less, the colony growth of nitrifying microorganisms on the media surface is slow, and the cultivation period (from the start of operation until the nitrifying microorganisms adhere to the media surface) is slow. period) is as short as two months,
At times, it could take up to four months. The reason why the cultivation period is longer in raw water with a BOD of 5mg/or less is because the activated sludge used for seeding did not contain many nitrifying microorganisms or because there was little inorganic carbon. I was not aware that the cause was poor adhesion of the nitrifying microorganisms to the medium. Therefore, in biological treatment using a biological fixed bed method for the purpose of nitrification of ammonia nitrogen, if you try to collect nitrifying microorganisms in raw water that contains ammonia nitrogen but has a BOD of 5 mg/or less, nitrification will not be possible as in the conventional method. Even if seeds are planted in activated sludge containing microorganisms or phosphorus, inorganic carbon sources, trace amounts of metal salts, etc. are added, the colonization period is excessively long because nitrifying microorganisms do not adhere well to the media surface. There was a drawback. The present invention uses the above biological fixed bed method to achieve BOD5mg/
The purpose of this method is to eliminate the drawbacks of conventional methods when nitrifying raw water containing ammonia nitrogen as described below, improve the adhesion of nitrifying microorganisms to the surface of the medium, and shorten the cultivation period. The present invention contains ammonia nitrogen and BOD5
mg/or less of raw water, under aerobic conditions, on a sprinkle bed,
In nitrification treatment in which ammonia nitrogen is oxidized to nitrate nitrogen or nitrite nitrogen by a biological fixed bed method in which nitrifying microorganisms are grown on the surface of a medium such as an immersed bed or a fluidized bed, during the cultivation period of the nitrifying microorganisms. A BOD source is added to the raw water, and the sticky force of the viscous substance secreted when BOD-degrading microorganisms adhere to the media surface is used to make it easier for nitrifying microorganisms with poor adhesion to adhere to the media surface, thereby inhibiting the growth of nitrifying microorganisms. It is characterized by speeding up the cultivation and shortening the breeding period. BOD here is BOD shown in JIS K0102.
This is due to the definition and measurement method. Further, the amount of the BOD source added to the raw water may be adjusted to 3 to 20 mg/, preferably 3 to 10 mg/, using the BOD measurement method described above. This is because when BOD is increased to 20mg/ or more, BOD-degrading microorganisms with a high growth rate become the priority species on the surface of the medium, inhibiting the growth of nitrifying microorganisms, and circulating raw water becomes contaminated. This is because there is a possibility that Also, if the BOD is less than 3mg/, the surface of the media
Since the growth of BOD-degrading microorganisms is slowed down, the effect of promoting the adhesion of nitrifying microorganisms due to the coexistence of BOD-degrading microorganisms is reduced. Next, embodiments of the present invention will be described based on the drawings. The first illustrated example is an embodiment in which only nitrification treatment is performed, and raw water 1 containing ammonia nitrogen with a BOD of 5 mg/or less is led to a regulating tank 2, where an alkaline agent 3 is added to make the pH 7-8, preferably PH 8-8. 8.5
and add BOD source 4. Furthermore, when there is little inorganic carbon in the raw water, an inorganic carbon source 5 is added. This raw water is then led to a nitrification tank 6 filled with granular media that is maintained in aerobic conditions by aeration and dissolution of air or high concentration oxygen-containing gas 7.
In order to inoculate nitrifying microorganisms at the beginning of the cultivation period, sludge containing nitrifying microorganisms may be put into the nitrification tank 6.
Inside this nitrification tank 6, the BOD of raw water 1 introduced is
The conditions are such that microorganisms that decompose components and nitrifying microorganisms that oxidize ammonia nitrogen are easily active, and BOD decomposing microorganisms that are highly adherent and grow rapidly adhere to the media surface at first, and then nitrifying microorganisms that are less adherent adhere to the media surface. It attaches and proliferates using the viscous substances secreted by BOD-degrading microorganisms. During the cultivation period, most of the outflow water 8 from the nitrification tank 6 is circulated and returned to the adjustment tank 2 to increase the chances of contact between the microorganisms in the outflow water 8 that cannot adhere to the medium and the medium. It is a good idea to do so. However, when the amount of microorganisms on the media surface increases and the ammonia nitrogen concentration in the effluent water decreases, this circulation rate can be reduced, and after the colonization period, this circulation can be stopped, resulting in BOD source 4. Addition becomes unnecessary. The second illustrated example is a mode in which a denitrification tank 10 is followed after the nitrification tank 6 to perform denitrification treatment, and in this case, as in the first illustrated example, raw water is newly added to the adjustment tank 2. Instead of adding BOD source 4,
It is possible to utilize residual amounts of organic carbon sources 9 such as methanol, glucose, and molasses in the outflow water that are added for the cultivation of denitrifying microorganisms in the denitrifying tank 10 under anaerobic conditions or for denitrifying treatment. be. That is, the denitrified water 1 that flows out after being added with the organic carbon source 9 and denitrified in the denitrifying tank 10
1 is circulated through adjustment tank 2, and the residual organic carbon is removed.
It is used as a BOD source to promote the growth of nitrifying microorganisms in the nitrification tank 6. As described above, according to the present invention, in a method for nitrifying raw water containing ammonia nitrogen and having a BOD of 5 mg/less or less by a biological fixed bed method under aerobic conditions, the growth of nitrifying microorganisms on the surface of the medium is It is possible to speed up the process, shorten the cultivation period, and perform wastewater treatment quickly and effectively. Next, examples will be shown. Example 1 A 10-fold dilution of ammonia-containing wastewater (NH ₄ ^- N = 50-85 mg/) with a BOD of 1.0-3.5 mg/ is used as raw water, and an immersion bed is filled with gravel of 10-12 mmφ to a height of 4 m. During the nitrification treatment, nitrifying microorganisms are attached to the gravel surface at the initial stage of water flow. The results of speed comparison are shown in Table 1. The experimental conditions during the agglomeration period were: dissolved oxygen concentration in raw water 37-40mg/, pH 8.5, and after addition of BOD source.
The BOD was 7 to 12 mg/, the rate of rise in the bed was 5 m/h, and the circulation ratio (flow water circulation amount/raw water amount) was 10.

[Table] As is clear from Table 1, the population of nitrifying microorganisms is faster in raw water with a BOD source added than in raw water with no BOD source added, and in the raw water with a BOD source, nitrifying microorganisms adhere to the NH ₄ - It takes 35 to 40 days for N to reach 1 mg/ or more, whereas
With raw water without BOD source additives, the period was 20-30% longer, over 50 days. Example 2 When nitrifying seawater containing approximately 1 mg BOD and 6 to 8 mg/NH ₄ -N using a fluidized bed method using granular activated carbon, nitrifying microorganisms were added to the surface of the activated carbon at the beginning of operation. Sludge containing nitrifying microorganisms (activated sludge) was mixed into the small amount of raw seawater mentioned above, and water was continuously passed through the seawater for 50 days under conditions of an upward flow rate of 30 m/h and a circulation ratio (effluent circulating water volume/raw water volume) of 5. However, the adhesion of nitrifying microorganisms to the surface of the activated carbon remained unsatisfactory, so water flow was continued for 30 days under the same water flow conditions while adding a glucose solution so that the BOD of raw seawater was approximately 10 mg/kg. The results were as shown in Table 2.

[Table] As is clear from Table 2, during the period without BOD source addition, even after 50 days have passed since the start of water flow, NH ₄ -N
However, when glucose solution was added as a BOD source, 2.5 mg/g was nitrified in 30 days.
NH ₄ −N nitrified by 190% from mg/ to 7.2 mg/
The amount of has increased. In this way, by adding a BOD source to the _NH4 -N containing raw water with low BOD during the cultivation period of nitrifying microorganisms, it is possible to accelerate the attachment of nitrifying microorganisms to the medium.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are system explanatory diagrams showing embodiments of the present invention, respectively. 1...Raw water, 2...Adjustment tank, 4...BOD source,
6... Nitrification tank, 8... Runoff water, 9... Organic carbon source, 10... Denitrification tank, 11... Denitrification treated water.

Claims (1)

[Scope of Claims] 1. A method for nitrifying raw water containing ammonia nitrogen and having a BOD of 5 mg/less or less by a biological fixed bed method in which nitrifying microorganisms are grown on the surface of a medium under aerobic conditions. A nitrification treatment method characterized by adding a BOD source to raw water during the cultivation period. 2 The addition rate of the BOD source added to the raw water is 3~
The nitrification treatment method according to claim 1, wherein the amount is 20mg/. 3. Claim 1, wherein the effluent from the nitrification treatment is circulated into the raw water during the cultivation period of the nitrifying microorganisms.
The nitrification treatment method according to item 1 or 2. 4. The nitrification treatment method according to claim 1 or 2, wherein the subsequent denitrification step effluent under anaerobic conditions is used as a BOD source to be added to the raw water.